Histamine H3 receptors are found inter alia on presynaptic terminals of peripheral nerves, where they modulate autonomic neurotransmission and modulate a variety of end organ responses under control of the autonomic nervous system. They are also heteroreceptors, modulating the release of numerous other neurotransmitters such as dopamine, glutamate, noradrenaline, serotonin, GABA, acetylcholine, some peptides and co-transmitters.
Recently numerous histamine H3 receptor ligands have been developed. An overview of the current advance in H3 ligand research and patenting is given in Expert Opin. Ther. Patents (2003) 13(6). Examples of Histamine H3 receptor ligands can be found in WO02/76925, WO00/06254, WO02/12190, WO02/12214 and WO02/06223.
H3 receptor ligands are believed to be suitable for the treatment of various diseases including both disorders of the central nervous system and inflammatory disorders. Examples of diseases where treatment with H3 ligands is believed to be useful are inflammatory bowel disease, Crohn's disease, colitis ulcerosa, sleep disorders, migraine, dyskinesia, stress-induced anxiety, psychotic disorders, epilepsy, Cognition deficiency diseases such as Alzheimer's disease or mild coginitive impairment, depression, mood disorders, schizophrenia, anxiety disorders, attention-deficit hyperactivity disorder (ADHD), psychotic disorders, obesity, dizziness, epilepsy, motion sickness, vertigo, respiratory diseases such as adult respiratory distress syndrome, acute respiratory distress syndrome, bronchitis, chronic bronchitis, chronic obstructive pulmonary disease, cystic fibrosis, asthma, emphysema, rhinitis, chronic sinusitis, allergy, allergy-induced airway responses, allergic rhinitis, viral rhinitis, non-allergic rhinitis, perennial and seasonal rhinitis, nasal congestion and allergic congestion.
Although H3 ligands are known there is still a need to provide new H3 ligands that are good drug candidates. In particular, preferred compounds should bind potently to the histamine H3 receptor whilst showing little affinity for other receptors. They should be well absorbed from the gastrointestinal tract, be metabolically stable and possess favourable pharmacokinetic properties. They should be non-toxic and demonstrate few side-effects.